X87: Clean up JSConstructStub.
X87: Clean up JSConstructStub.

port 882055ff6a58f6b585575229f40f364e5f2a3ad0 (r29082).

   The original CL covers part of X87 port. This CL addes the missing changes.

original commit message:

  - fix truthfulness of comments
    - use InitializeFieldsWithFiller more consistently
    - use unsigned comparisons for pointers

    No change in functionality intended.

    Bonus: improve JavaScriptFrame::Print() for an enhanced debugging experience:

BUG=

Review URL: https://codereview.chromium.org/1210153007

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#29397}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh